Certain objects on a web page are immune to layering and will always appear on top (or 'through') a layer placed above them by z-index. These objects include form select lists, iframes, applets and, of course, flash movies. The only way around this (that I'm aware of) is to hide the offending object while the covering layer is visible, and then reveal it again when the covering layer is hidden. There's an example of this at: